The invention relates to a multi-trailer combination or train having two or more connected trailers, powered by a tractor, or No. 1 element. One object of the invention is to minimize the oscillatory yaw behavior and rollover tendency between the second or last trailer or No. 4 element and its steerable axle or No. 3 element. An additional object of the invention is to prevent "jackknifing" between the pulled trailers of the multi-trailer assembly or combination.
Numerous types of trailer dolly and hitch arrangements are known in the prior art as being adapted to allow one trailer to be hitched to and pulled behind another trailer, and these prior art dolly and hitch arrangements are mainly responsible for the problems or lack of stability experienced by the multi-trailer combinations.
The majority of dollies or rotatable wheeled vehicles (No. 3 elements) used for coupling multi-trailer combinations, have no means to prevent or limit rotation of the No. 3 element in a horizontal plane about the hitch point on the rear of a pulling trailer. These conventional dollies are provided with a hitch on the forward end of the drawbar which allows the dolly or No. 3 element to freely pivot in such horizontal plane. Additionally, stability against rollover, i.e., pivoting about a longitudinal horizontal axis, of the last trailer or No. 4 element with respect to the towing or first trailer or No. 2 element is exceptionally low because the No. 3 element has a conventional trailer coupler, of fifth wheel, above the axle which is pivotally engaged with the towed or second trailer or No. 4 element in the same manner as the conventional fifth wheel on the tractor or No. 1 element is pivotally engaged with the first trailer or No. 2 element. Thus, the last trailer or No. 4 element receives no roll support from the lead or towing semi-trailer, particularly in evasion type maneuvers.
The steering stabilizer of the present invention is applicable to all multi-trailer tractor combinations, but it finds special application for tandem or double-bottom tankers because of their unique stability problems. Double tankers typically carry approximately 9,000 gallons of fuel in the lead or towing tanker and approximately 7,000 gallons of fuel in the trailer or second tanker. The No. 2 element by law is the heaviest vehicle of the so-called train. The obvious reason for using tandem tankers is to reduce the number of tractors and operators required, theoretically reducing the likelihood of accidents and decreasing costs including costs of operation.
Unfortunately, the rollover stability and away stability of known double bottom tanker combinations is exceptionally low, particularly in accident evasion type maneuvers. This problem is accentuated because, unlike other multi-trailer combinations, the tandem tankers are frequently towed when they are only partially loaded with fuel. The sudden movement or sloshing of the fuel within the tankers during high speed or emergency maneuvers drastically decreases the roll and sway stability of the last trailer or No. 4 element. It is not uncommon for the No. 4 element or second trailer to overturn and explode, resulting in a serious highway accident with resultant loss of life, limb, and property.
The double tanker combination has definite stability problems, with the primary problem residing in the behavior of the second trailer or No. 4 element of the train. In emergency lane change maneuvers, the second trailer amplifies the yaw motions of the tractor and towing trailer. At a high frequency range of steering inputs, the second trailer or No. 4 element experiences roll or overturning accelerations which are more than twice as large as that experienced at the tractor or No. 1 element. In addition to oscillatory yaw behavior, the second trailer has a low level of basic rollover immunity. In a steady turn situation, the rollover limit of the loaded second trailer is approximately 20% lower than that exhibited by most heavy commercial vehicles. For emergency lane changes, the double tanker will experience rollover at a maneuvering level which is less than half of the maneuvering level that is needed to roll over conventional tractor, semi-trailer combinations. Thus, the known double tanker combination exhibits an exceptionally low degree of yaw and roll stability with the second trailer or No. 4 element contributing most significantly to the problem.
The dynamic stability of a multi-trailer tractor combination involves not only its resistance to oscillatory yaw and rollover but also its resistance to jackknifing, i.e., the inadvertent gross longitudinal misalignment of the trailers about the vertical pivot axis connection between the tractor and the lead trailer or between the lead trailer and the trailing or second trailer. Jackknifing or buckling occurs when a semi or full trailer pushes its towing vehicle in such a manner that a very acute angle results between the units. The jackknifed condition frequently leads to a disastrous loss of control which is a hazardous problem when the roadway is slick from rain or ice.
The prior art has attempted to prevent jackknifing by various means such as trailer brakes which are actuated by the tractor operator from the tractor cab in an emergency situation. For tandem trailers, the trailers must be prevented from pivoting about their vertical pivot axis connection into a longitudinally misaligned condition. Otherwise, the momentum of the swerving trailer causes the two trailers to close upon one another as blades of a jackknife.
It is accordingly the general objective of the present invention to provide a rollover and jackknife-resisting apparatus between a lead or towing trailer (No. 2 element) and a towed or second trailer (No. 4 element) which minimizes oscillating yaw behavior of the second trailer, provides roll support from the lead trailer to the second trailer, and increases the basic rollover immunity of the second trailer.